Structural characteristics of copper/hydrogenated amorphous carbon composite films prepared by microwave plasma-assisted deposition processes from methane–argon and acetylene–argon gas mixtures

Abstract

Copper/hydrogenated amorphous carbon (Cu/a-C:H) composite films have been deposited on silicon substrates by a hybrid technique combining microwave plasma-assisted chemical vapor deposition and sputter-deposition from methane–argon and acetylene–argon gas mixtures. The major objective of this work was to investigate the effect of the carbon gas precursor on the structural characteristics of Cu/a-C:H composite films deposited at ambient temperature. The major characteristics of CH 4–argon and C 2H 2–argon plasmas were analyzed by Langmuir probe measurements. The composition of films was determined by Rutherford backscattering spectroscopy, energy recoil detection analyses and nuclear reaction analyses. The carbon content in the films was observed to vary in the range 20–77 at.% and 7.5–99 at.% as the CH 4 and C 2H 2 concentrations in the gas phase increased from 10 to 100%, respectively. The atom number ratio H/C in the films was scattered approximately 0.4 whatever the carbon gas precursor used. The crystallographic structure and the size of copper crystallites incorporated in the a-C were determined by X-ray diffraction techniques. The copper crystallite size decreased from 20 nm in pure copper films to less than 5 nm in Cu/a-C:H films containing more than 40 at.% of carbon. Grazing incidence small angle X-ray scattering measurements were performed to investigate the size distribution and distance of copper crystallites as functions of the deposition parameters. The structural characteristics of copper crystallites were dependent on the hydrocarbon gas precursor used. The crystallite size and the width of the size distribution were homogeneous in films deposited from CH 4. Copper crystallites with an anisotropic shape were found in films deposited from C 2H 2. The major radicals formed in the plasma and condensed on the surface of growing films, namely CH and C 2H radicals for films produced from CH 4 and C 2H 2, respectively, play probably a crucial role in the growth mechanism of copper crystallites embedded in the a-C:H matrix.